1. Field of the Invention
The present invention relates to a method for forming an overlapping section in which a first workpiece and a second workpiece are overlapped by the aid of an adhesive or sealant material.
2. Description of the Related Art
Conventionally, when constructing an internal combustion engine for an automobile, a packing made of rubber is interposed between metal members, for example, between an oil pan and a cylinder block. Such packing avoids leakage of oil and/or gas from spaces between the cylinder block and the oil pan.
However, since the packing is made of rubber, it is deteriorated as time elapses. Therefore, it is feared that leakage could occur after passage of a sufficiently long period of time. For this reason, a polymer sealant material, which tends not to suffer from time-dependent changes, and which makes it possible to avoid leakage over a long period of time, has begun to be adopted. Silicone rubber is one example of such a polymer sealant material.
The polymer sealant material is applied, for example, to a cylinder block, and in this state, an oil pan is overlapped thereon. Of course, it is also permissible that a polymer packing may be used and allowed to intervene between other overlapping sections.
Various oils, such as rust-preventive oils, cutting oils, and press working oils, tend to adhere to the respective constitutive members, such as the cylinder block and the oil pan, which make up the automobile internal combustion engine. If such members are overlapped with each other in a state in which the oil has adhered thereto as described above, the seal becomes incomplete, because such oil reduces the wettability of the polymer sealant material surface with respect to the overlapping section.
In order to avoid the inconvenience described above, oil adhering to parts to which the polymer sealant material is applied must be wiped off beforehand, or another type of degreasing treatment must be performed beforehand to the parts. However, in this case, if the wiping or degreasing treatments are performed non-uniformly, the seal is incomplete and ineffective at such non-uniform portions. Further, in the case of such wiping or degreasing treatments, it is necessary to perform complicated manual operations, resulting in an increase in cost.
Japanese Laid-Open Patent Publication No. 6-192625 suggests a procedure whereby a part, having oil adhered thereto, is irradiated with ultraviolet light, including light beams having predetermined wavelengths, before applying a polymer sealant material or an adhesive to the part. It is first described that irradiation using ultraviolet light may cut or break down the oil molecules to produce lower molecular weight molecules, which exhibit improved compatibility between the adhesive and the converted oil having lower molecular weight molecules, and thus wettability may be improved. Secondly, it is indicated that polar groups and/or reactive groups may be produced during break down of the oil molecules, and thus the oil itself may function as a coupling agent, enhancing the adherence of the adhesive and the sealant material. For the reasons described above, when the adhesive surface is reformed by ultraviolet radiation, adherence of the overlapping section in which the adhesive or the polymer sealant material intervenes, is performed favorably, and adhesive strength and sealing performance are improved (see Paragraph [0021] of such publication).
However, even when ultraviolet light is radiated as described above, it is still impossible to confirm, in all cases, sufficient adhesive strength and sealing performance at the overlapping section.